Pumps commonly used to pump molten metal include transfer pumps and discharge pumps as disclosed in the publication "H.T.S. Pump Equation for the Eighties" by High Temperature Systems, Inc., which is incorporated herein by reference in its entirety.
A transfer pump transfers molten metal out of one furnace to another furnace or into a ladle. In a transfer pump a tubular riser extends vertically upward from the base chamber to the motor mount and contains a passageway for molten metal. Support posts are also provided between the base and the motor mount.
A discharge pump transfers molten metal from one bath chamber through a submerged pipe to another bath chamber. Such a pump typically includes a shaft sleeve and support posts between the base and the motor mount, but has no riser.
As shown in FIG. 1, pumps which employ a base 11 may either be top feed pumps or bottom feed pumps depending, among other things, on the configuration of the base 11 and orientation of the impeller vanes 12 relative to the direction of shaft 17 rotation. Multiple impellers 13 and volute openings 14 may be used, as disclosed in U.S. Pat. No. 4,786,230 to Thut, issued Nov. 22,1988, which is incorporated herein by reference in its entirety.
Pumps used for pumping molten metal typically include a motor carried by a motor mount, a shaft 17 connected to the motor at one end, and an impeller 13 connected to the other end of the shaft 17. Such pumps may also include a base 11 with an impeller chamber 21, the impeller 13 being rotatable in the impeller chamber 21. Support members extend between the motor mount and the base 11 and may include a shaft sleeve 18 surrounding the shaft 17, support posts (not shown), and an optional tubular riser 19. As shown in FIG. 2, a spiral-shaped volute member 20 may be employed in the impeller chamber 21 to form a spiral-shaped volute opening 14 surrounding the impeller 13. During pump operation, the volute opening 14 advantageously produces a higher molten metal outflow pressure than an impeller chamber 21 without a volute opening 14. This is especially important with pumps employing a tubular riser 19 or for pumping high specific gravity molten metals such as zinc or lead. Molten metal is directed from the volute opening 14 to a molten metal outlet 22 or 25 with enough pressure to be expelled at an effective flow rate from the molten metal outlet 22 or 25. In transfer pumps, the pressure created by the volute opening 14 is sufficient to push the molten metal to the outlet 22 and up the entire length of the vertically oriented tubular riser 19. A disadvantage to the use of a separate volute member 20 is that the volute member 20 can become unattached within the impeller chamber 21 and move, thereby affecting molten metal flow through the pump.
Pumps may be designed with pump shaft bearings (not shown), impeller bearings (not shown) and with bearings 23 in the base 11 that surround the impeller to avoid damage of the shaft 17 and impeller 13 due to contact with the shaft sleeve 18 or base 11. The shaft 17, impeller 13, and support members (not shown) for such pumps are immersed in molten metals such as aluminum, magnesium, zinc, lead, copper, iron and alloys thereof The pump components that contact the molten metal are composed of a refractory material such as graphite or ceramic.
The typical base shown in FIGS. 1, 2 and 3 includes the impeller chamber 21, and at least one molten metal inlet 26 and outlet opening 22 or 25. The impeller chamber 21 houses the impeller 13 and generally includes the spiral-shaped volute member 20. An egress channel 27 extends from the impeller chamber 21 toward the molten metal outlet 22 or 25. The impeller chamber 21 of the base 11 may further contain upper (not shown) and/or lower annular bearing rings 23 to prevent damage to the pump components from direct contact of the impeller 13 with the base 11 during operation of the pump. The lower bearing ring 23, for example, may be carried by an annular lower base portion 24 which is cemented to the base around its periphery and may be pinned in place. The lower portion of the impeller 13 is normally generally coplanar with the bottom portion of the base 11 and the bottom portion of the lower annular bearing ring 23. The bearing ring 23, volute member 20 and posts (not shown) are typically cemented in place.
A common problem during operation of molten metal pumps employing a base of this type is the frequency with which catastrophic failure occurs as a result of the volute member 20 and/or annular lower bearing 23 pushing through the bottom of the base. This can occur in top or bottom feed pumps and requires immediate repair. It is believed that the pressure load from the molten metal bath and the molten metal contained in the impeller chamber 21 on the volute member 20 and/or annular lower bearing 23 causes this failure. Repairs of this type are expensive and time consuming and require taking the equipment out of operation.
Manufacturing and construction of a base 11, such as in a transfer pump, typically involves drilling openings through the top and bottom portions of the base 11 for the impeller 13, drilling an opening at the top portion of the base 11 for receiving the shaft sleeve 18 and drilling an opening for a molten metal outlet 22 or 25. If the pump is designed to have a lower annular bearing ring 23, the lower base portion 24 is disposed in a lower opening 29. The lower base portion 24 and the volute member 20 are separately manufactured. The lower base portion 24 is recessed to receive the annular bearing 23. The volute member 20 is spiral-shaped and positioned in the impeller chamber 21 to form a volute opening 14. Extending from the volute opening 14 is an egress channel 27 formed in the base 11. The distal portion of the egress channel 27 extends to the molten metal outlet 22 or 25. The bearing 23, the lower base portion 24 and the volute member 20 are typically cemented into position. In order to complete the egress channel 27 of a transfer pump, labor intensive hammer and chisel work is required to remove the portion of the base shown as 30 in FIGS. 1 and 2 to enable the molten metal inlet 26 to be in communication with the molten metal outlet 22.